1. Field
This disclosure is concerned generally with the filtration of blood products and specifically with the filtration of white blood cells from platelets.
2. Prior Art
The advantages of removing white blood cells (WBCs) from blood components such as red blood cells (RBCs) and platelets are known. See, for example, U.S. Pat. No. 4,596,657 to Wisdom (removal of WBCs from RBCs). The removal of WBCs from platelets is disclosed in U.S. Pat. No. 4,857,190 to Kuhlemann et al. and in articles by Sirchia, G. et al. Vox Sang. 44:115-120, 1983, and Kickler, T. S. et al., Transfusion 29:411-414, 1989.
Existing methods remove WBCs from the final form of platelet concentrates (PC) or pools of such concentrates. See the Kuhlemann et al. patent which describes a platelet pooling bag designed for this purpose. Sirchia et al. disclose WBC removal after storage of a PC. Kickler et al. disclose filtration of a PC at the bedside, just before infusion into a patient. Before these existing methods can be used, however, the PC must be available. Unfortunately, the collection and initial processing of whole blood from a donor may result in a delay in the preparation of PCs.
In current practice at least two centrifugation steps are used to make a PC from whole blood. In the first step whole blood is collected in a blood bag and then centrifuged to form a lower, dense portion of RBCs and an upper, less dense portion of plasma which is rich in platelets and known as platelet rich plasma (PRP). The upper PRP is then expressed from the bag into a second bag which is centrifuged to form a lower, denser platelet pellet and an upper, less dense plasma portion known as platelet-poor plasma (PPP). The upper PPP is then expressed from the second bag for use in preparing various plasma products (e.g. albumin, immunoglobulins, coagulation factors and the like) leaving behind the plasma pellet or PC.
Even after the PC is made, however, it may be stored for some time (e.g., up to 5 days) before it is filtered to remove WBCs.
The presence of WBCs in a stored PC is thought to result in WBC degradation products that can adversely affect the platelets and their environment. Unfortunately, in conventional blood banking processes, there have been no available means for pre-storage removal of WBCs from platelets in a closed system. Thus, PCs, if filtered at all, have commonly been filtered just prior to infusion into the patient.
We have found that it is now possible to remove substantially all WBC's from a platelet product prior to platelet storage. This is done by filtering platelet rich plasma (PRP), preferably soon after it is formed from centrifuged whole blood, using the novel closed system described below. In a preferred embodiment the filtration of WBCs from the PRP occurs within 8 hours of whole blood collection from a donor.